The invention relates to a fastener with a shank, with a head at one end of the shank intended for welding to a workpiece, and with at least one detent pawl formed on the shank that extends radially outward from the shank toward the head and that is elastically resilient in the radially inward direction, wherein the shank has a longitudinal hole in which is located a stud, and wherein one end of the stud projects out of the longitudinal hole and forms the head.
Fasteners of the specified type may be used in automotive manufacture, among other applications, for example in order to attach trim panels to the floor, walls, doors or roof of a motor vehicle body. The fasteners are meant to attach the trim panels tightly and durably to the relevant body part while additionally permitting the easiest and most economical installation possible of the paneling.
A fastener of the aforementioned type is known from DE 10 2004 031 342 A1. It has a sleeve-like outer part and an inner part which can be inserted therein, both of which parts are made of plastic, wherein the inner part has a longitudinal hole into which is screwed a stud that has an external thread, and the head of said stud forms a weldable end. The prior art fastener consists of three separate parts and consequently is relatively expensive to manufacture and install. Moreover, it has a relatively great axial length, which limits the possibilities for its application.
Known from DE 19,929,924 A1 is a single-piece fastener that can be made of plastic and has a leg section with a foot that is designed to be welded to a workpiece, and that has two elastic engagement claw sections arranged on opposite sides of the leg section extending diagonally outward from the end of the leg section to the foot section and are capable of being bent radially inward, wherein the engagement claw sections each have an engagement step designed as an inward recess. This fastener is only suitable for welding to plastic parts. It also has the disadvantage that the axial free clamping length is dependent on the formation of the weld joint, so attachment without play is only possible when the trim panel to be attached has sufficient elasticity.
One aspect of the invention is to create a fastener of the aforementioned type which is easy and economical to manufacture, and permits easy installation. In addition, another aspect of the feature is retention of the components to be fastened may be free of play in the axial direction and is independent of the formation of the weld joint.
According to an aspect of the invention, the fastener comprises a shank, a head at one end of the shank that is intended for welding to a workpiece, and at least one detent pawl formed on the shank that extends radially outward from the shank toward the head and that is elastically resilient in the radially inward direction and that has on its outside an engagement recess with a radial and an axial support surface, wherein the shank has a longitudinal hole in which is located a stud, wherein one end of the stud projects out of the longitudinal hole and forms the head, and wherein a flange that is elastically resilient in the axial direction, whose outermost edge region is located opposite the engagement recess of the detent pawl, is formed on the shank.
Depending on the material of the workpiece that the fastener is to be welded to, a stud made of a suitable material, such as steel, aluminum, or plastic, may be inserted in the shank. The shank, detent pawl and flange of the fastener may be made of a thermoplastic material.
Moreover, another aspect of the fastener is to make it possible to fasten a component, for example a trim panel of a motor vehicle, in a manner that is vibration-proof and free of play, since said panel can be clamped in place between the resilient flange and the support surfaces of the detent pawl independent of the formation of the weld joint. All that is necessary to install a component to be fastened is to place the component's fastening opening on the welded-on fastener and to press on it until it latches into the engagement recess of the detent pawl. After the latching, the trim panel is held without play by the elastically resilient flange in the axial direction and by the elastic detent pawl in the radial direction relative to the shank. The design of the engagement recess ensures here that the detent pawl engages in the opening of the trim panel and braces itself outward in the radial direction in the trim panel opening.
In one embodiment, the fastener according to the invention has three detent pawls, which are formed on the shank and are separated from one another by gaps, wherein the outside surfaces of the detent pawls constitute segments of a common truncated cone surface and wherein the radial support surfaces of the detent pawl engagement recesses lie on a common cylindrical surface that is coaxial to the surface of the truncated cone. During installation, this design facilitates positioning of a component to be fastened having a circular fastening opening, while also ensuring precisely positioned attachment of the component by the fastener.
Easy manufacture of the fastener is made possible according to another proposal of the invention in that the flange is recessed in the area of the axial projection of the detent pawls. This measure makes it possible to mold the unit consisting of shank, detent pawls, and flange as a single piece using a two-part, and thus simple, mold tool.
In the case of a metallic stud, welding on of the fastener may be accomplished by means of an electric welder using the drawn arc method. It is necessary here to bring the stud into contact with a conductor to deliver the welding current. For this purpose, the head of the stud can have, between its weldable end and the shank, a contact section for placement of welding tongs. If the desired axial length of the head is too small to form a contact section, provision can be made according to another aspect of the invention for openings to be formed in the radial direction in the wall of the shank that are freely accessible from outside, and that open onto the longitudinal hole. Welding tongs or a contact element can be brought into contact with the stud through these openings.
If the stud is provided with an external thread and is screwed into the longitudinal hole of the shank, a tool engagement region for placement of a screwdriver or wrench can be provided on the end of the shank opposite the head. By this means, the attachment of a component can be released in a simple manner by unscrewing from the stud the unit consisting of the shank, detent pawls and flange.
Another possibility for detaching a retained component from the fastener consists in using a suitable tool, for example a tube, to bend the detent pawls far enough inward that they release from the retained component.
In welding devices for welding similar components, it has proven useful to feed these components to the welding device either singly or in groups through a plastic tube by means of compressed air. In this connection, plastic tubes with a round cross-section as well as profile tubes are used. In the latter, the inside tube profile corresponds to the envelope profile that the component to be conveyed has when it is in a suitable feed position. However, the use of a profile tube results in limitations on the mobility of the welding device on account of the high stiffness of such a tube, so feeding through a round tube may be advantageous. The fastener according to the invention is not suitable “as is” for feeding through a round tube, however, since it does not have appropriate guide surfaces to guide and stabilize the fastener in a suitable feed position with the longitudinal axis oriented in the feed direction. In order to nevertheless make feeding through a round tube possible, according to another proposal of the invention coupling elements are provided at the end of the shank opposite the head that are suitable for gripping the head of a second fastener. If multiple fasteners of this type are arranged coaxially and in the same orientation one after the other, then they make up a chain composed of multiple fasteners supported by the coupling elements, and this chain can be conveyed through a round tube without any problem, with the fasteners being guided by the edge of their flanges.
If it is also desirable for fasteners according to the invention to be singly conveyable through a round tube, this can be accomplished according to another proposal by guide elements that axially extend the outside contour of the flange and that have an axial length sufficiently long that the fastener can be conveyed with its longitudinal axis coaxial to the tube axis through a conveyor tube with a round cross-section in a positionally stable manner and without a tendency to jam. The guide elements are connected in a separable manner to the fastener by means of predetermined breaking points. In an advantageous embodiment, the guide elements can consist of multiple axially parallel rods arranged on the circumferential edge of the flange. Another suitable embodiment provides for the guide elements to consist of plates which are arranged radially on the detent pawls or shank and which have axially parallel outer guide edges. In place of, or in addition to, the guide elements, a guide disk of the same diameter as the flange may be arranged a suitable distance from, and parallel to, the flange, being attached to the shank or guide elements in a separable manner by means of predetermined breaking points.